pub enum Infallible {}
Expand description
The error type for errors that can never happen.
Since this enum has no variant, a value of this type can never actually exist.
This can be useful for generic APIs that use Result
and parameterize the error type,
to indicate that the result is always Ok
.
For example, the TryFrom
trait (conversion that returns a Result
)
has a blanket implementation for all types where a reverse Into
implementation exists.
impl<T, U> TryFrom<U> for T where U: Into<T> {
type Error = Infallible;
fn try_from(value: U) -> Result<Self, Infallible> {
Ok(U::into(value)) // Never returns `Err`
}
}
§Future compatibility
This enum has the same role as the !
“never” type,
which is unstable in this version of Rust.
When !
is stabilized, we plan to make Infallible
a type alias to it:
pub type Infallible = !;
… and eventually deprecate Infallible
.
However there is one case where !
syntax can be used
before !
is stabilized as a full-fledged type: in the position of a function’s return type.
Specifically, it is possible to have implementations for two different function pointer types:
trait MyTrait {}
impl MyTrait for fn() -> ! {}
impl MyTrait for fn() -> std::convert::Infallible {}
With Infallible
being an enum, this code is valid.
However when Infallible
becomes an alias for the never type,
the two impl
s will start to overlap
and therefore will be disallowed by the language’s trait coherence rules.
Trait Implementations§
1.34.0 · source§impl Clone for Infallible
impl Clone for Infallible
source§fn clone(&self) -> Infallible
fn clone(&self) -> Infallible
1.0.0 · source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read moresource§impl<T> Context<T, Infallible> for Option<T>
impl<T> Context<T, Infallible> for Option<T>
use anyhow::{Context, Result};
fn maybe_get() -> Option<T> {
...
}
fn demo() -> Result<()> {
let t = maybe_get().context("there is no T")?;
...
}
1.34.0 · source§impl Debug for Infallible
impl Debug for Infallible
1.34.0 · source§impl Display for Infallible
impl Display for Infallible
1.8.0 · source§impl Error for Infallible
impl Error for Infallible
source§fn description(&self) -> &str
fn description(&self) -> &str
1.30.0 · source§fn source(&self) -> Option<&(dyn Error + 'static)>
fn source(&self) -> Option<&(dyn Error + 'static)>
§impl Error for Infallible
impl Error for Infallible
1.34.0 · source§impl From<!> for Infallible
impl From<!> for Infallible
source§fn from(x: !) -> Infallible
fn from(x: !) -> Infallible
1.34.0 · source§impl From<Infallible> for TryFromIntError
impl From<Infallible> for TryFromIntError
source§fn from(x: Infallible) -> TryFromIntError
fn from(x: Infallible) -> TryFromIntError
1.36.0 · source§impl From<Infallible> for TryFromSliceError
impl From<Infallible> for TryFromSliceError
source§fn from(x: Infallible) -> TryFromSliceError
fn from(x: Infallible) -> TryFromSliceError
1.44.0 · source§impl Hash for Infallible
impl Hash for Infallible
1.34.0 · source§impl Ord for Infallible
impl Ord for Infallible
source§fn cmp(&self, _other: &Infallible) -> Ordering
fn cmp(&self, _other: &Infallible) -> Ordering
1.21.0 · source§fn max(self, other: Self) -> Selfwhere
Self: Sized,
fn max(self, other: Self) -> Selfwhere
Self: Sized,
1.34.0 · source§impl PartialEq for Infallible
impl PartialEq for Infallible
1.34.0 · source§impl PartialOrd for Infallible
impl PartialOrd for Infallible
1.61.0 · source§impl Termination for Infallible
impl Termination for Infallible
impl Copy for Infallible
impl Eq for Infallible
Auto Trait Implementations§
impl Freeze for Infallible
impl RefUnwindSafe for Infallible
impl Send for Infallible
impl Sync for Infallible
impl Unpin for Infallible
impl UnwindSafe for Infallible
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
source§impl<T> CloneToUninit for Twhere
T: Clone,
impl<T> CloneToUninit for Twhere
T: Clone,
source§unsafe fn clone_to_uninit(&self, dst: *mut T)
unsafe fn clone_to_uninit(&self, dst: *mut T)
clone_to_uninit
)§impl<Q, K> Comparable<K> for Q
impl<Q, K> Comparable<K> for Q
§impl<Q, K> Equivalent<K> for Q
impl<Q, K> Equivalent<K> for Q
§fn equivalent(&self, key: &K) -> bool
fn equivalent(&self, key: &K) -> bool
§impl<Q, K> Equivalent<K> for Q
impl<Q, K> Equivalent<K> for Q
§fn equivalent(&self, key: &K) -> bool
fn equivalent(&self, key: &K) -> bool
key
and return true
if they are equal.source§impl<T> IntoAnyhow for T
impl<T> IntoAnyhow for T
source§fn into_anyhow(self) -> Error
fn into_anyhow(self) -> Error
self
into an anyhow::Error
.